1. Field of the Invention
The present invention relates to a wireless communication device, especially, a wireless communication device used in an RFID (Radio Frequency Identification) system, and a manufacturing method of a wireless communication module defining the wireless communication device.
2. Description of the Related Art
An RFID system as a management system for articles has recently been developed according to which communication is executed in a non-contact manner between a reader/writer that generates an induction electromagnetic field and an IC tag that has predetermined information stored therein (hereinafter, referred to as “wireless communication device”) attached to an article to transmit information. The wireless communication device used in the RFID system uses an antenna having any one of various shapes depending on the use thereof. When the shape of the antenna is changed, the value of the impedance of the antenna for the wireless IC chip is also varied and an impedance matching circuit has to be designed depending on the shape of the antenna.
In an ordinary wireless communication device, an impedance matching circuit is disposed on a base material film that has an antenna element disposed therein. The impedance matching circuit is fabricated by mounting chip parts such as an inductor and a capacitor each having a proper element value, or forming as a pattern an inductor, a capacitor, and the like each having a proper element value on the base material film.
The wireless communication device is attached to each of various articles and is used in each of various use environments. When the impedance matching circuit is fabricated on the same base material film as that of the antenna element, the impedance matching circuit is influenced depending on the type of the article (especially, the relative permittivity thereof) and the use environment. As a result, a defect arises that the value of the impedance is shifted and the loss is increased (the communication distance is shortened).
An approach according to which an impedance matching circuit is incorporated in a multi-layer substrate other than a film that has an antenna disposed thereon, and the multi-layer substrate is mounted on the antenna is described in Japanese Patent No. 4561932. With this approach, the impedance matching circuit surely tends to avoid any influence of the external environment. The antenna however can take any of various shapes and plural multi-layer substrates need to be prepared depending on the shape of the antenna, that is, the number of line-ups of the multi-layer substrate needs to be increased resulting in an increase of the labor for designing the multi-layer substrate and the labor for stock management.
Especially, when the impedance matching circuit is configured using a rewiring layer of the wireless IC chip, the wireless IC chip cannot be used for any other use and the degree of difficulty is therefore increased for the production management and the stock management.